Trying to install a CB in a Ford Explorer?

I've installed a CB in my ford explorer running the antenna coax from a magnetic base on the top rear and running the coax through the rear door hatch. i had a friend tune it and i reached a good 15 miles. but after closing the hatch and drove away i tried to talk to my installer and it was all garbled. i could hear him for awhile until i started hearing some static. did i route my antenna coax wrong and pinched it? if so, is there a way to route the cable under the belly of the explorer and up through a hole somewhere as to not pinch it in anyway??